Despite being composed of relatively simple nucleotide building blocks, nucleic acids are capable of encoding a vast array of information: witness the human genome encodes all the information necessary for the synthesis and assembly of all the components of the human body from the neural networks of the brain to the intricate structures of the skeleton, tissues and organs. Nucleic acids include deoxyribonucleic acid (DNA) and the more labile ribonucleic (RNA). Since nucleic acid sequences can be unique and complex, utilization of these particular characteristics in solving several common coding problems, such as authenticating and tracking products and detecting counterfeit products, has recently attracted great interest.
Many product manufacturers utilize apparent qualities and definitive designs identifiable as “trade dress” to uniquely identify their high quality and high value products and thereby earn the trust of their customers. Others also add labels for anti-counterfeit purposes. Traditional anti-counterfeiting labels are generally formed from materials having particularly targeted physical or chemical characteristics, for example, magnetic strips on checkbooks, laser holographs on credit cards, fluorescent ink on stock certificates, and heat-sensitive inks on confidential documents. Anti-counterfeiting labels have also been made by adding specific antigens to objects that need to be identified, the antigens can then be detected with an antibody specific for the antigen. However, antigens and antibodies are proteins with characteristically poor stability under many environmental conditions of temperature and humidity, and are prone to denaturation or even degradation and consequently lose activity and can easily be destroyed, thereby reducing the accuracy and reliability of identification.
Thus, nucleic acids, such as, for example, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) which encode essential hereditary information have been looked to as an improved alternative to commonly used anti-counterfeiting labels and markers. DNA and RNA are polymers consisting of a chain of nucleotides, referred to as “oligonucleotides” consisting of relatively short chains of up to say, twenty to fifty bases in length, or “polynucleotides” for longer chains. These oligonucleotide or polynucleotide chains consist of a number of nucleotides linked together in sequence like beads on a string. Each nucleotide consists of a ribose sugar-phosphate linked to one of only four kinds of nitrogenous bases: adenine (often represented in abbreviated form as “A”), guanine (represented as “G”), cytosine (represented as “C”) and thymine (represented as “T”) in the case of DNA; and adenine (A), guanine (G), cytosine (C) and uracil (U) in the case of RNA. The oligonucleotides or polynucleotides share the same sugar-phosphate backbone. The 3′-hydroxyl group on the ribose sugar is covalently bonded to the 5′-phosphate group of its neighboring nucleotide to form a chain structure with the planar nitrogenous bases protruding from the chain not unlike the teeth of a comb.
The bases A, T, G and C in one oligonucleotides or polynucleotides chain are each capable of specific-pairing with another base a different chain to form a double stranded structure, or with the same chain to form a double stranded loop or hairpin structure: Adenine specifically bonds with thymine through two hydrogen bonds in DNA (or with uracil in RNA) and cytosine specifically bonds with guanine through three hydrogen bonds. That is, T will bond to A and G to C bringing two nucleotide chains together to form a double strand, or two parts of a single nucleotide chain together to form a double stranded region with each strand of the duplex connected by a loop.
An additional advantage of nucleic acids for use as markers or taggants is that with the appropriate proper protection these molecules can be preserved for long periods of time. Evidence from preserved specimens in glaciers, ice sheets, tar pits and bogs and marshes shows that DNA is resilient to degradation over thousands, and in some cases millions of years. Such evidence has been used to deduce information concerning the ancestry and origins of ancient peoples as well as of plants and animals. Protected marker DNA can also be stabilized in polymers for coating of high value articles or objects of interest so as to survive long periods of time and can then used for identification, authentication and tracking purposes. This ability to persist over long periods of time coupled with very sensitive methods to detect low numbers of molecules for instance by amplification using the polymerase chain reaction (PCR), makes nucleic acids, and DNA in particular, an attractive candidate for use as a marker. Moreover, nucleic acids offer an almost unlimited coding capacity since the number of possible unique sequences increases fourfold with every additional base of the sequence of the oligonucleotide or polynucleotide.
Sheu et al. (U.S. Pat. No. 7,115,301) disclosed that DNA can be used to mark solid articles or substances by incorporating DNA into a variety of media that may be used for coating all or only part of an item of interest. Several media useful for such coatings disclosed by Sheu et al. include polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), and polypropylene (PP), or acrylic/epoxy resin-based formulations. Often times a non-invasive or non-destructive sampling method is required for tagging of precious articles, such as paintings or fragile articles, to preserve the aesthetic appearance and the integrity of the marked articles. However, the recovery of the taggant may be difficult or may provide such a low yield as to limit the applicability of the method.
Polymers such as acrylic or epoxy based resinous polymers can be used as the carrier media for taggants. Unfortunately, recovery of taggant from these polymers is often difficult and combinations of solvents have been developed to deal with such issues (see for instance, Elwell, U.S. Pat. No. 4,278,557). However, for most applications employing the use of such polymers as coatings, total dissolution of the polymer is not necessary (nor is it usually possible) in order to achieve adequate recovery of the taggant from the polymer coating for verification purposes. Furthermore, the use of such solvents on precious articles or objects to which the polymer is adhered may tarnish or damage the article or object and is undesirable and is usually discouraged. An owner or a bona fide purchaser interested in authentication of a purchase is unlikely to approve the use of significantly invasive or destructive methods.
Therefore, there is a need in the art for a system permitting retrieval of taggants from polymerized coating on an article of value without subjecting the tagged article to rigorous solvent treatments which may disturb the aesthetics of the article.